The Contract Pin: Guarding Human-Owned Sections in Free-Model Doc Drafts

The marginal cost of drafting documentation approaches zero when you can call a free model endpoint from a free server, but that cost drop does not change where trust must remain. Every generated line that touches an API contract, a configuration default, or an error code becomes a liability if it is not verified by a human. The working compromise is to let models draft the prose while pinning the contract blocks to human ownership and enforcing that pin in CI.

Free model access removes the financial obstacle to regenerating long docs on every request. You can spawn a draft, inspect it, discard it, and retry without watching cloud charges accumulate. The remaining bottleneck is not token price; it is review bandwidth, because the failure modes of generated docs are semantic, not lexical. A model might rephrase a default value, swap an argument name, or add an example that quietly changes the expected behavior.

MonkeyCode's free model access and free server option make this iterative loop genuinely cheap, and that availability changes the economics of documentation work. Teams can afford to ask many questions of the model before a human looks at a single diff. The danger is that the cheap loop also encourages accepting what the model says, which is why the ownership boundary must be encoded as a machine-checked rule rather than a style guideline. Disclosure: This article was prepared as part of MonkeyCode's product outreach.

The workflow in five steps

1. Wrap every contract-like section in PIN markers.
2. Write a prompt that instructs the model to leave those markers unchanged.
3. Generate the draft using the free model endpoint.
4. Run ownership_gate.py to produce or update the lock file.
5. Merge only after the gate passes and a human reviews the unpinned diff.

Define the Pin

Start by wrapping every region that describes a verifiable fact in a machine-readable marker. The syntax matters less than the consistency; choose a marker that cannot appear inside code blocks and that your CI script can parse reliably. The common pattern in Markdown is an HTML comment, which remains invisible in the rendered page but easy to extract.

<!-- PIN: create-item -->
### POST /v1/items

- **Parameters**: `name` (string, required), `ttl` (integer, default 300)
- **Errors**: `400`, `429`, `500`

<!-- END PIN -->

Only humans may update the content between the markers. The model receives instructions to treat those blocks as opaque, and the CI gate verifies that instruction was followed. If the model ignores the instruction, the changed hash fails the build and the pull request cannot merge.

Hand the Model a Scoped Prompt

Your prompt should not ask the model to rewrite a whole file. It should point at the free-form sections and explicitly forbid any change to the pinned regions. A minimal prompt looks like this:

You are writing documentation for the endpoint below.

Generate only the "Usage" and "Troubleshooting" sections.

Preserve verbatim every character inside the `<!-- PIN: ... -->` blocks.
Do not add, remove, or reword any of those lines.

{endpoint specification}

The key is the negative instruction combined with the marker. Models are reasonably good at following a negative constraint when the target is visually distinct, but you cannot trust that compliance is perfect. The CI gate provides the second layer of assurance.

Run the Gate in CI

Save the following script as ownership_gate.py in your repository. It extracts all pinned blocks, hashes their content, and compares the hashes to a lock file that represents the last human-approved version.

#!/usr/bin/env python3
import argparse
import hashlib
import re
import sys
from pathlib import Path

PIN_RE = re.compile(r'<!-- PIN: ([\w-]+) -->(.*?)<!-- END PIN -->', re.S)

def extract_blocks(text):
    return {m.group(1): m.group(2).strip() for m in PIN_RE.finditer(text)}

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('doc')
    parser.add_argument('lockfile')
    parser.add_argument('--update', action='store_true')
    args = parser.parse_args()

    text = Path(args.doc).read_text(encoding='utf-8')
    blocks = extract_blocks(text)
    if not blocks:
        print('No PIN blocks found.', file=sys.stderr)
        return 2

    current = {name: hashlib.sha256(content.encode()).hexdigest()
               for name, content in blocks.items()}

    approved = {}
    lock_path = Path(args.lockfile)
    if lock_path.exists():
        for line in lock_path.read_text(encoding='utf-8').splitlines():
            digest, name = line.split(None, 1)
            approved[name] = digest

    if args.update:
        lock_path.write_text(''.join(f'{digest} {name}\n' for name, digest in sorted(current.items())),
                             encoding='utf-8')
        print('Lock file updated.')
        return 0

    failed = False
    for name in current:
        if name not in approved:
            print(f'New PIN block "{name}" has no approved record.', file=sys.stderr)
            failed = True
        elif approved[name] != current[name]:
            print(f'PIN block "{name}" differs from the approved version.', file=sys.stderr)
            failed = True

    for name in approved:
        if name not in current:
            print(f'PIN block "{name}" was removed.', file=sys.stderr)
            failed = True

    if failed:
        return 1

    print('All PIN blocks match the approved state.')
    return 0

if __name__ == '__main__':
    sys.exit(main())

To record the initial approved state, run python3 ownership_gate.py docs/api.md docs/api.lock --update. Humans must run this command deliberately after their review. Any subsequent change to a pinned block without an update fails the next CI run.

name: ownership-gate
on: pull_request
jobs:
  ownership:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: python3 ownership_gate.py docs/api.md docs/api.lock

The gate runs on every pull request, but it does not block a human from updating a contract. It simply requires that the change pass through the --update path, which is the point where a reviewer is present.

What to Pin: A Decision Table

Section	Pin?	Reason
API endpoint paths	Yes	Wrong path breaks clients
Parameter names and types	Yes	Type mismatches cause runtime failures
Default values	Yes	Silent behavior changes
Error codes	Yes	Error-handling logic depends on them
Configuration keys	Yes	Deployment and orchestration rely on them
Prose introductions	No	Low mutation risk
Usage examples	No, but run them	Examples must be executed, not only reviewed
Troubleshooting FAQ	No	Failure cost is lower and rephrasing is acceptable

Pinning is not about hiding information from models; it is about marking the regions where generated wording becomes a contractual promise. An endpoint path, a default value, and an error code are promises that clients depend on. Prose explanations and FAQ entries are also promises, but their failure cost is lower, and they benefit from the model's ability to rephrase.

Limitations

The gate verifies that pinned blocks match their approved hashes, but it cannot verify the semantic truth of unpinned content. A model can write a fluent paragraph that subtly contradicts a pinned specification, and the gate will not notice. Free model access also means variable latency and occasionally incoherent output, so the loop still requires a human to read unpinned sections. The approach assumes the lock file is maintained honestly; if reviewers run --update without reading the diff, the protection collapses.

Who Should Not Use This

Teams writing low-level protocol documentation or legal compliance texts should not rely on this workflow, because the cost of a subtle error in those domains is too high to offload to an unverified model. Teams with only two or three documentation pages might find the script over-engineered compared to a manual diff review. The workflow pays off when documentation volume is large enough that a human review of every generated sentence is the bottleneck.

Conclusion

The combination of free model endpoints and free servers turns documentation iteration into a cheap loop. The responsibility that does not get cheaper is separating model-draftable prose from human-owned contracts. A marker, a prompt, and a CI gate convert that responsibility from aspiration into an enforced mechanism.